When I'm killing, my music taste changes depending on what class I'm playing.

Warrior - My favorite song to listen to is 'Valhall Awaits Me' by Amon Amarth, it is beyond epic.
Ret Paladin - Toss up between 'Starfall/Illusion' by Dragonland and 'Emerald Sword' by Rhapsody of fire
Mage/Lock - Anything by Celldweller